Lipid Incorporation During Experimental Decay of Arthropods - Biopolymers: A Molecular Paleontology Approach - page 109

the corresponding Larmor frequencies of 1 H and 13 C are ~300 and 75 MHz,
respectively. All experiments were performed using a 5 mm double resonance probe
with zirconia rotors. 1 H- 13 C cross polarization was employed utilizing a RF ramp
protocol on the 13 C channel. The 1 H 90° pulse width was 4

μ s and high power decou-

pling (w1/2 = 75 kHz) was employed during signal acquisition. The Magic Angle

spinning frequency (wr/2

π

) was 11.6 kHz. The contact time was determined from a
standard of chitin to optimum at 6 ms. A recycle delay of 2 s was chosen to mini-
mize longitudinal interference during signal averaging. Typically 36,000 acquisi-
tions were obtained per sample.

π

Changes in Gross Morphology During Decay

The shrimp and cockroach showed a sequence of morphological decay stages similar
to that recorded in previous experiments (Briggs and Kear 1994 ; Duncan et al. 2003 ).
The shrimp cephalothorax separated from the abdomen within 2 weeks and the
cuticle was easy to remove. The muscle tissue in the abdomen, however, remained
relatively solid. The scorpion and cockroach remained intact, but the abdomen of the
latter was visibly bloated and the soft tissue inside both had largely liquifi ed. Within
4 weeks the shrimp disarticulated completely on removal from the vessel; the cuticle
had become very thin and brittle but some soft tissue remained in the posterior abdo-
men. The scorpion skeleton was still intact and remarkably robust although the soft
tissue had largely decayed away. The cockroach skeleton largely disarticulated when
the specimen was removed from the vessel; some tissue remained inside but was not
intact structurally. Within 24 weeks the scorpion skeleton remained intact, the cock-
roach cuticle showed some thinning on the ventral side and very little cuticle could
be recovered from the shrimp. At 44 weeks there was little further change, but one
scorpion appendage separated from the rest of the exoskeleton

Changes in Ultrastructure During Decay

Figure 6.1 documents the key changes observed during decay of shrimp and scor-
pion cuticle as observed by SEM. Figure 6.1a shows the cross section of the unde-
cayed shrimp cuticle and Fig. 6.1b that after 44 weeks decay reveling loss of
exocuticle and reduction in thickness. Figure 6.1d shows the surface of the unde-
cayed shrimp cuticle and Fig. 6.1e that after 44 weeks of decay showing extensive
loss of the exocuticle exposing the endocuticle underneath. The loss of exocuticle
commenced within 4 weeks of decay in the shrimp cuticle. In contrast, the scorpion
and cockroach cuticle showed little change in the ultrastructural features after decay.
Figure 6.1c shows the cross section of the scorpion cuticle after 44 weeks decay and
Fig. 6.1f the surface after 44 weeks decay where no obvious change was observed
from the undecayed samples.